The present invention relates to a method for controlling the profile of a plate workpiece being rolled on a hot rolling mill in a finishing stage.
For controlling the profile of a workpiece on a practical rolling mill, a coil obtained posterior to a take-up process is partly cut off to measure the profile of the product workpiece, and in accordance with the actual value thus measured, an operator carries out adjustment of a rolling pitch (attained principally by delaying the rolling pitch), adjustment of the workpiece thickness in the roughing stage, adjustment of the rolling load distribution in the finishing stage, adjustment of the pressure (with respect to wedge and crown) on both the driving side and working side of the rolling mill, adjustment of the workpiece temperature by controlling a delay time on a delay table, modification of the initial curve of the mill rollers, intermediate rearrangement of the mill rollers, and adjustment of the quantity of cooling water for the finishing mill rollers, thereby controlling the profile of the workpiece on the rolling mill to desired dimensions. However, since such actual measurement of the profile is carried out in an off-line manner posterior to take-up of the workpiece, it requires a relatively long time. Besides that, profile producing factors are so complicated and are liable to cause great undesirable effects due to secular changes including thermal crown and abrasive wear of the rollers, so that the rolling conditions are not readily maintained constant to result in difficulties in attainment of accurate crown control. Moreover, the abovedescribed rolling pitch adjustment brings about a reduction in the rolling efficiency and also a great time delay in cooling or heating the rollers of the finishing rolling mill to render difficult the crown control for individual coils.
The inventions proposed heretofore in relation to profile control are principally of the type employing a roll bending system, in which the profile control allowance obtained by roll benders is so small that sufficient control is not achieved by the roll benders alone.
U.S. Pat. No. 3882709 to Kawamoto, Toshiharu et al. discloses a method for controlling the profile of workpieces on rolling mills, which comprises the steps of roughly adjusting the crown by means of a first roughing stage of the rolling mill to produce a profile on the workpiece which is within an allowable predetermined range for a successive second finishing stage of the rolling mill and finely adjusting the crown by means of said second finishing stage of the rolling mill to produce the desired profile on the workpiece by utilizing all but the final stand within said finishing stage.
In the method, the crown is controlled by adjusting the roll temperatures of the stands, the roll benders, the rolling pitches at the stands, and/or modifying the load distribution among the stands.
In the above invention, however, there still exist some disadvantages as observed in the foregoing prior arts, and preferably such disadvantages are to be eliminated.